Project Summary/Abstract Systemic lupus erythematosus (SLE) is a devastating autoimmune disease in which autoantibodies to ubiquitous nuclear antigens cause inflammation and tissue damage in multiple organs. The treatment of SLE has improved considerably over the past 30 years, but these advances have relied on existing medications with insufficient efficacy and significant toxicities. Although several new therapeutics are advancing to Phase 2 and 3 trials, only one modestly effective biologic is currently FDA approved for treating active SLE. It is imperative, therefore, that advances in immunologic knowledge be applied to improve the treatment and quality of life of SLE patients. Autoantibody production is central to the pathogenesis of SLE but many questions remain about the origins of the plasma cells that produce them. It is clear that autoantibody production can precede disease onset by many years, and that flares of SLE are often associated with a new wave of plasma cell proliferation. Our Autoimmunity Center of Excellence proposal is centered on the hypothesis that an improved understanding of the mechanisms of induction and source of autoantibodies in individual patients will allow us to define the spectrum of dysregulated mechanisms responsible for loss of tolerance in human SLE and will form the basis for appropriate patient stratification and selection for clinical trials. To this end, we will apply new technologies that allow meaningful study of small numbers of human cells in a native repertoire to revisit basic questions about the origin and regulation of autoantibodies in SLE. A crucial tool is a new fluorescent nuclear antigen preparation, developed by the Diamond lab that can be used to identify and isolate autoreactive B cells that represent only a small fraction of the total B cell population. This will facilitate the use next generation sequencing of immunoglobulin genes to analyze the repertoire specifically of autoreactive B cells. The Principal Project will characterize autoreactive plasma cells from patients with SLE and ask about their origins and transcriptional profile, with a view to identifying distinct pathways of activation in individual patients that may be specific to autoreactive B cells, compared with cells that protect against microbial antigens. The Collaborative Project will examine mechanisms for the initiation of lupus-related autoimmunity in patients being treated with TNF inhibitors for inflammatory arthritis. The Pilot Project will address the transcriptional, metabolic and functional diversity of circulating T follicular helper cells in patients with SLE and ask whether it is possible to restore normal B cell helper function of these cells by altering T cell metabolism. Our proposal is bolstered by close scientific interactions among the three lead investigators, by collaborations with experts in next generation sequencing methods and data analysis and by a robust clinical infrastructure that will add clinical depth and ensure timely recruitment of patients for all three studies.